1. Field of the Invention
This invention relates to a fibrous polyamide substrate having durable resistance to staining by acid colorants and to a method of rendering a fibrous polyamide substrate durably resistant to staining by acid colorants.
2. Description of Prior Art
Fibrous polyamide substrates, such as nylon carpeting are susceptible to staining by both naturally occurring and commercial acid colorants found in many common foods and beverages. The demand for reduced staining from such acid colorants has by and large been met previously by treatment with compositions comprising sulfonated napthol and or phenol or sulfonated phenol-formaldehyde condensation products as disclosed for example in the following patents: U.S. Pat. No. 4,501,591, Ucci and Blyth; U.S. Pat. No. 4,592,940, Blyth and Ucci; U.S. Pat. No. 4,680,212, Blyth and Ucci; U.S. Pat. No. 4,780,099, Creshler, Malone and Zinnato; and U.S. Pat. No. 4,865,885, Herlant and Al, or by treatment with compositions comprising sulfonated novalak resins together with polymethacrylic acid as disclosed in U.S. Pat. No. 4,822,373 (Olson, Chang and Muggli). The use of polymers or copolymers of methacrylic acid of low weight average molecular weight and low number average molecular weight is described in U.S. Pat. No. 4,937,123 (Chang, Olson and Muggli).
The initial stain resistance properties imparted to polyamide substrates, such as carpeting, that have been treated using the above mentioned compositions degenerate significantly with each wet cleaning the substrate receives. Improved stain resistance after wet cleaning can be achieved by increasing the amount of the phenolic resin in the stain resist product or by increasing the amount of stain-resist product initially applied to the substrate, however, this generally leads to discoloration caused by yellowing of the substrate initially and further discoloration upon exposure to oxides of nitrogen and/or light. This discoloration in most cases is attributed to dihydroxydiphenol sulfone and its associated SO.sub.2 group.
Stain resist products currently available in the market place are generally novalak--type resins based on dihydroxydiphenyl sulfone and phenol sulfonic acid condensed with aldehyde in acid media, or dihydroxy diphenyl sulfone and naphthalene sulfonic acid condensed with aldehyde at low pH.
It is generally known that increasing the ratio of dihydroxydiphenyl sulfone to the phenol sulfonic acid or napththalene sulfonic acid increases the stain resistance properties of the resin and subsequently causes a higher degree of yellowing or discoloration initially and further discoloration upon exposure to oxides of nitrogen and/or light.
It is also evident that when the ratio of phenol sulfonic acid or naphthalene sulfonic acid to dihydroxydiphenyl sulfone increases, the result is lower stain-resist properties and less discoloration.
The addition of acrylic polymers and/or copolymers to the previously mentioned novalak resin condensation products as disclosed in U.S. Pat. No. 4,822,373 (Olson, Chang and Muggli) allows the use of a novalak resin in small quantities and larger quantities of the acrylic resin. With this combination of novalak resin and acrylic resin, big improvement in the light fastness or less discoloration is achieved due to the dramatically reduced percentage of novalak resin in the product mentioned above which is adjusted to obtain a desired minimum level of discoloration while maintaining a maximum level of durability to wash. The high level of initial stain resistance is supplied primarily by the methylacrylic polymer and/or copolymer and after wet cleaning the stain resistance is supposedly maintained by the novalak resin, the acrylic having largely been removed during the wet cleaning process.